The present invention is directed generally to magnetic recording media and devices incorporating the media and, more particularly, to manganese (Mn) containing layers for use with cobalt or cobalt alloy based magnetic layers in the formation of magnetic recording media.
There is an ever increasing demand for magnetic recording media with higher storage capacity, lower noise and lower costs. To meet this demand, recording media have been developed with increased recording densities and more well-defined grain structures that have substantially increased the storage capacity, while lowering the associated noise of the recording media. However, the rapid increases in recording densities over the last two decades, combined with the proliferation of personal computers have only served to fuel the demand for even higher storage capacity recording media having lower noise and cost.
Magnetic discs and disc drives are commonly used to provide quick access to vast amounts of stored information. Both flexible (floppy)and rigid (hard) discs are available. Data are stored in magnetic bits in segmented circular tracks on the discs. Disc drives typically employ one or more discs rotated on a central axis. A magnetic head, or slider, is positioned over the disc surface to either access or add to the stored information. The heads for disc drives are mounted on a movable arm that carries the head in very close proximity to the disc over the various tracks and segments.
The structure of a typical thin film disk is multilayered and includes a substrate at its base covered by an underlayer, a magnetic layer and optionally, an overlayer at the top. The overlayer may be coated with an overcoat and an organic lubricant.
The magnetic layer is the main body on which the magnetic bits are recorded. Recording media comprised of cobalt or cobalt alloy-based magnetic films having a chromium or chromium alloy-based underlayer deposited on a nonmagnetic substrate have become the industry standard.
Magnetic properties, such as coercivity (H.sub.c) , remanant magnetization (M.sub.r) and coercive squareness (S*), are crucial to the recording performance of the Co alloy thin film. The magnetic properties are primarily dependent on the microstructure of the film for a fixed composition. For thin film longitudinal magnetic recording media, the desired crystalline structure, or texture, of the Co and Co alloys is hexagonal close packed (HCP) with uniaxial crystalline anisotropy and a magnetization easy direction along the c-axis predominately in the plane of the film (i.e, in-plane). Usually, the better the in-plane c-axis crystallographic texture, the higher the coercivity of the Co alloy thin film used for longitudinal recording. High coercivity is required to achieve a high remanence. Likewise, for perpendicular magnetic recording media, the desired crystalline structure of the Co alloys is HCP with the uniaxial anisotropy and crystalline c-axis perpendicular to the film plane. For very small grain sizes coercivity increases with increased grain size. Large grains, however, results in greater noise. There is a need to achieve high coercivities without the increase in noise associated with large grains. To achieve a low noise magnetic medium, the Co alloy thin film should have uniform small grains with grain boundaries which can magnetically isolate neighboring grains. This kind of microstructure and crystallographic texture is normally achieved by manipulating the deposition process, by grooving the substrate surface, by varying the cobalt alloy composition or by the proper use of an underlayer.
Cobalt-based alloys as opposed to pure cobalt are commonly used in longitudinal and perpendicular magnetic media for a variety of reasons. For example, non-magnetic elements such as Cr are commonly bulk doped into the magnetic film to lower the magnetization. This is especially important in perpendicular media where the demagnetization energy associated with the magnetic moment of the alloy must be less than the magneto-crystalline anisotropy energy in order for the magnetization to be oriented perpendicular to the media film plane. The same technique is used in longitudinal magnetic media to lower the flux transition demagnetization energy, resulting in a shorter flux transit-on length and, hence, higher recording densities. Even more importantly, however, non-magnetic elements are introduced into the Co-alloy to limit the magnetic exchange coupling between cobalt grains. It is believed that preferential diffusion of elements such as Cr, Ta, P, B, or Si from the bulk of the magnetic grain to the grain boundaries during film growth help to isolate the individual grains by reducing the magnetic exchange coupling between grains. This then results in a significantly lower media noise. For example, Deng et al. found that the addition of small amounts of Ta to CoCr alloys resulted in the increased Cr diffusion to the grain boundaries. See Youping Deng, David N. Lambeth, and David E. Laughlin, "Structural Characteristics of Bias Sputtered CoCrTa/Cr Films", IEEE Transactions on Magnetics, Vol. 29, no. 5, September 1993, pp. 3676-3678.
Underlayers can strongly influence the crystallographic orientation, the grain size and as discussed herein the chemical segregation at the Co alloy grain boundaries. Underlayers which have been reported in the literature include Cr, Cr with an additional alloy element X (X=C, Mg, Al, Si, Ti, V, Co, Ni, Cu, Zr, Nb, Mo, La, Ce, Nd, Gd, Tb, Dy, Er, Ta, and W), Ti, W, Mo, NiP and B2-ordered lattice structures, such as NiAl and FeAl. While there would appear to be a number of underlayer materials available, in practice, only a very few work well enough to meet the demands of the industry. Among them, the most often used and the most successful underlayer is pure Cr.
For high density longitudinal recording, in plane orientation has heretofore been achieved by grain-to-grain epitaxial growth of the HCP Co alloy thin film on a body centered cubic (BCC) Cr underlayer. The polycrystalline Co-based alloy thin film is deposited with its c-axis, the [0002] axis, either parallel to the film plane or with a large component of the c-axis in the film plane. It has been shown by K. Hono, B. Wong, and D. E. Laughlin, "Crystallography of Co/Cr bilayer magnetic thin films", Journal of Applied Physics 68 (9) p. 4734 (1990), that BCC Cr underlayers promote grain-to-grain epitaxial growth of HCP Co alloy thin films deposited on these underlayers. The heteroepitaxial relationships between Cr and Co which bring the [0002] axis down or close to the film plane are (002).sub.cr //(110).sub.Co,(110).sub.Cr //(101).sub.Co, (110).sub.Cr //(100).sub.Co, and (112).sub.Cr //(100).sub.co. Different Co/Cr epitaxial relationships prevail for different deposition processes. To obtain a good BCC structure which promotes the formation of the HCP structure, the Cr underlayer should be thicker than about 50 .ANG..
Likewise, to achieve perpendicular high density recording media, the perpendicular orientation of the Co c-axis with respect to the film plane has usually been obtained by grain-to-grain epitaxial growth of the HCP Co alloy thin film to an oriented HCP underlayer of (0002) crystalline texture or a face centered cubic (FCC) crystal underlayer of (111) crystalline texture. Ti and Ti.sub.90 Cr.sub.10 at % are often cited as the best seed layers for this purpose, although other seed layers, such as Pt, CoO/Pt and non-magnetic CoCr35at % have been used to induce this structure. See "Development of High Resolution and Low Noise Single-layered Perpendicular Recording Media for High Density Recording", IEEE Trans. Magn., Vol. 33, no. 1, p. 996-1001 (January. 1997); "Compositional separation of CoCrPt/Cr films for longitudinal recording and CoCr/Ti films for perpendicular recording" IEEE Trans. Magn., Vol. 27, no. 6, part 2, pp. 4718-4720 (1991); "Properties of CoCrTa Perpendicular films prepared by sputtering on Pt underlayer", J. MMM, Vol. 155, no. 1-3, pp. 206-208 (1996); IEEE Trans. Magn. Vol. 32, no. 5, pp. 3840-3842 (September. 1996); IEEE Trans. Magn. Vol. 30, no. 6, pp. 4020-4022 (November. 1994); and, "Development of High Resolution and Low Noise Single-layered Perpendicular Recording Media for High Density Recording", IEEE Trans. Magn. Vol. 33, no. 2, pp. 996-1001) (January. 1997).
U.S. Pat. No. 4,652,499 discloses efforts to improve the underlayer of longitudinal magnetic media by adding vanadium (V) to Cr to change its lattice constant and thereby to promote a better lattice matching between the HCP Co alloys, such as CoPt or CoPtCr, and the BCC CrV underlayer. In addition, U.S. Ser. No. 08/315,096 now U.S. Pat. No. 5,693,426, which is incorporated herein by reference, discloses a new group of underlayers including materials having a B2-ordered crystalline structure, such as NiAl and FeAl.
Additional improvements in the structure of the magnetic layer have been found when incorporating intermediate layers between the underlayer and the magnetic layer. Also, seed layers can be incorporated between the underlayer and the substrate to provide additional control of the structure of the underlayer and to prevent contamination of the underlayer by the substrate contaminants. The seed layers, underlayers, and intermediate layers are collectively referred to herein as the underlayer structure. In addition, multiple magnetic layers that may or may not be separated by a Cr inner layer are sometimes employed to produce variations in the magnetic properties of the resulting film. The magnetic layers and intervening inner layers are collectively referred to herein as the magnetic layer structure.
The use of multi-layered underlayer and magnetic layer structures can provide for increased control over the grain size, the grain to grain epitaxial growth of subsequent layers and the surface roughness of the magnetic layers. However, the use of additional layers may also increase the overall cost and complexity of the manufacturing process.
The need for lighter, smaller and better performing and less costly computers with greater storage density demands higher density recording media for use in hard disk drives, other magnetic storage devices, and other applications. It is an object of the present invention to meet those demands with a magnetic recording media having high coercivity and low noise.